Residue Biochemical Identity Regulates Early Soil Fertility Recovery in Semi-Arid Agroecosystems of Erbil, Kurdistan Region, Iraq

Abstract

Soil productivity in semi-arid agroecosystems is constrained by prolonged organic matter depletion and nutrient limitation, yet residue-quality–driven fertility pathways remain poorly resolved under field conditions. The objective of this study was to evaluate the effect of different plant residue types on soil fertility and nutrient dynamics in a semi-arid agroecosystem in Erbil, Kurdistan Region, Iraq. We evaluated nine biochemically distinct plant residues (fruit-, woody-, and mixed-derived) applied at 2% (w/w) in a field experiment and quantified short-term shifts in soil physicochemical properties over 60 days. Residue incorporation significantly enhanced soil fertility compared to the control (p < 0.05), with responses strongly influenced by residue biochemical quality. Fruit and mixed residues, particularly Vitis vinifera and Punica granatum, increased soil organic carbon (2.10%), total nitrogen (0.19%), available phosphorus (27%), micronutrient availability, and soil moisture, while slightly reducing pH (6.95–6.70), improving nutrient solubility. Principal Component Analysis explained more than 90% of total variance, indicating a strong residue-quality fertility gradient. These findings demonstrate that residue biochemical characteristics play a key role in regulating early soil fertility processes and provide a practical strategy for improving soil quality in semi-arid environments.